Just as a strong personal statement can get you in, a poor personal statement/essay can quickly eliminate you from the mix. When a medical school committee has a few hundred applicants, seeing typos, spelling mistakes or bad content will quickly move you to the bottom of the pile. The personal statement is a quick way to "weed out" similar applicants. With two similar applications, the personal statement can decide who gets an interview and who does not.
2. Make excuses _ Lots of applicants have weaknesses in their application files, especially in their transcripts. Maybe you got low grades your freshman year. Maybe you had to leave school and work for a while. Maybe you got an F in that statistics class and had to retake it. Or maybe you got a degree in one field and are applying to grad school in a different field; or you didn't pass your medical residency exams the first time. Whatever your weakness is, do not offer excuses and do not bad_mouth anyone. So it wasn't your fault that the professor lost your final exam and flunked you, or jobs dried up in your original field of study, or you had the flu when you took the GRE. Don't say anything that sounds like an excuse or sounds like you are blaming someone else for you failing to achieve a goal. Even when it is true, it may make you seem whiny and unable to accept responsibility for your actions. Instead, address the weakness at the end of your statement, and explain how you have overcome it, learned from it, and are a better candidate now because of it.